1. Field of the Invention
The present invention relates to a gas barrier multi-layer film excellent in impact resistance and transparency as a packaging material for food, chemicals, electronic parts, etc.
2. Description of the Related Arts
Since polyamides obtained by polycondensation reaction of xylylenediamine with aliphatic dicarboxylic acids, such as a polyamide obtained from meta-xylylenediamine and adipic acid (hereinafter sometimes referred to as "MX nylon"), exhibit a low permeability to gaseous substances, such as oxygen and carbon dioxide, in recent years, they are used for bottles and oriented films as a gas barrier material.
However, generally the impact resistance is unsatisfactory if only a barrier layer made of the above barrier material is used. Therefore, practically, as a means for improving the impact resistance, a multi-layer film made up of (1) a polyamide layer made of MX nylon or a blend material of MX nylon and an aliphatic polyamide and (2) an adhesive layer made of a modified polyolefin is disclosed in Japanese Patent Application Laid-Open No. 119984/1978. However, the above polyamide layer made up of MX nylon or a blend material of MX nylon and an aliphatic polyamide has a problem that generally when the polyamide layer is heat-treated, it is hard to retain the good transparency.
Thus, an unorientated film of MX nylon itself is easily blushed and loses the transparency when it is subjected to sterilization by heating or absorbs water or moisture. Therefore, with the intention of keeping the transparency of the film, U.S. Pat. No. 4,908,272 discloses a barrier laminate wherein use is made of a barrier layer made of a non-crystalline polyamide whose diamine component is meta-xylylenediamine. However, such a non-crystalline polyamide is special, expensive, and so on and therefore is difficultly available, and the film obtained therefrom is rigid and so on and therefore has not been put to practical use.
Japanese Patent Application Laid-Open No. 120168/1992 and U.S. Pat. No. 5,268,219 disclose a technique wherein MX nylon and an aliphatic polyamide, such as nylon 6, are blended under specific conditions to obtain an unorientated film good in transparency. However, it is hard to say that when a blend of MX nylon with nylon 6 is used for an unorientated film, it has a satisfactory impact resistance. Thus, for example, on account of its low impact strength an unorientated multi-layer film obtained by the co-extrusion of a blend material of MX nylon with nylon 6 and a polyolefin has not yet been employed widely in the field of packaging except for special applications.
Namely, a gas barrier multi-layer film having satisfactorily both impact resistance and transparency after heat treatment is not known.